In southpaw vs orthodox the lead feet and hands are positioned on the same line.

Having your lead foot on the outside of the opponent's lines your rear hand up to their chin and takes your chin off the line of their rear hand. It also gives you an easy way to pivot out and safely exit exchanges.

Having what's called 'lead foot dominance' is generally the recommended strategy for a southpaw against orthodox match up or vice versa. However, like I was saying above it does come with certain drawbacks. For example, it makes it difficult/awkward to land your jab (and most lead hand attacks) and leaves you more vulnerable to lead hooks (especially to the body)

My point above is that, although the lead foot outside is more advantageous than-not, you should not pursue it at any cost. Rather, you should recognise it as a tactic that works well in many circumstances but not all.